CONTROL OF THE EUROPEAN CORN BORER OSTRINIA NUBILALIS HB. (LEPIDOPTERA: PYRALIDAE) BY TRICHOGRAMMA EVANESCENS (WESTWOOD) AND BACILLUS THURINGIENSIS IN CORN FILED AT KAFR EL-SHEIKH GOVERNORATE

CONTROL OF THE EUROPEAN CORN BORER OSTRINIA NUBILALIS HB. (LEPIDOPTERA: PYRALIDAE) BY TRICHOGRAMMA EVANESCENS (WESTWOOD) AND BACILLUS THURINGIENSIS IN CORN FILED AT KAFR EL-SHEIKH GOVERNORATE.

Nader. A. Abd El Razek

Plant Protection Research Institute, Agriculture Research Center, Dokki

ABSTRACT

A biological program was applied on Nili maize plantation of 2018 and 2019 by releasing the egg parasitoid, Trichogramma evanescens (two releases at rate of overall 55000 parasitoids/ release/ feddan at 7-day interval) and applying Bacillus thuringiensis var. kurstaki to control O. nubilalis. Releasing at a rate of 55000 wasps / feddan induced rate of parasitism in Trichogramma and Trichogramma combined with B. thuringiensisplots by 72.87 and 70.69 % in 2018 and by 75.12 and 73.67 % in 2019.in the combined treatment (T+B.t), the mean percentages of infestation by O. nubilalis larvae at harvest were 15 and 20 % in 2018 and 2019, respectively showing a reduction in the infestations to ears by 70 % and 66.67 % in the two years, respectively. One Bacillus thuringiensis treatment was not sufficient to prevent the larval attack to maize plants. This treatment led to lower reduction of mean number of larvae/15 plants (31.13 % and 34.09 %) and% reduction in infestation to ears by (10 % and 16.67 %) as compared to the control in 2018 and 2019.

INTRODUCTION

In Egypt  maize plants are subjected to infestation with a variety of insect pests, of which the most destructive one isOsterinianubilalis. Highest infestation to maize plants by this pest occurs during Nili cultivations Simeada, (1985). Larvae of this pest feed inside maize therefore, this pest may be considered the most serious economic pest of maize.

Normally, the mentioned pest is controlled according to the recommendations of the Egyptian Ministry of Agriculture by spraying Lannate 90% sp at a rate of 300 gm/feddan. But, investigating other non-chemical control methods is necessary, to be used either alone or in IPM programs to reduce the well-known harms due to environmental pollution by pesticides.

One alternative to synthetic insecticides is Bacillus thuringiensis a bacterium that produced δ-endo toxins specific to lepidopteran larvae. As a ubiquitous soil-borme bacterium,  B. thuringiensis has few detrimental effects on non target organisms, such as fish or mammals B. thuringiensis against the pest; such as McGuire, et al., (1994) David & William, (1995) and Ebaid, (2001).

Trichogramma spp. are active egg parasitoids of a wide range of lepidopterous pests and hence received considerable attention from numerous authors (Lingren 1970; Parker et al., 1971; Dysart 1972 and Oatman and Platner 1978). They are employed against O. nubilalis  in grain sweet and seed maize crops for which chemical control is difficult and not always effective (Bigler and Brunetti 1986). The efficacy of Trichogrammaspp. against O. nubilalis eggs in field depends on parasitoid searching ability, host preference and tolerance to environmental conditions (Hassan 1990). Pesticides may also negatively affect Trichogrammaspp. in the field. Most tested chemical insecticides were extremely toxic to the adult stage of Trichogrammaspp. (Stinneret al., 1974), but microbial pesticides were found to be fully compatible with Trichogrammaspp..Hassan et al., (1983) stated that B. thuringiensis was harmless to TrichogrammasppBartels and Hutchison (1995) controlled O. nubilalisin sweet corn with aerial applications of B. thuringiensis, and low rates or reduced numbers of applications of permethrin. The present paper summarizes the results of release of 55000 wasps of T. evanescens and one application of B. thuringiensis separately or combined for controlling O. nubilalis in maize fields.

MATERIAL AND METHODS

Field experiments were conducted in 2018 and 2019 Nili plantation to test the efficacy of program including release T. evanescensand spraying B.thuringiensis for controlling O. nubilalis.Two sites of about ½ feddan each (at Beila District, Kafr El-Sheikh Governorate) were chosen at a distance of 500 m. between them to prevent migration of the beneficial wasps from site of release to the other site. The area was divided into 16 equal plots that received 3 treatments and control of 4 replicates in randomized block design. Maize seeds (Giza 2 variety) were sown at a rate of 2-seeds/ hill on July 15^th. All plots received the normally recommended agricultural practices. Four plots of the site that did not receive Trichogramma release were left free of any treatment as a control while the other 4 plots received one application of Dipel 2x. Four plots of the site of release received one application of Dipel combined with release of T. evanescens. The other4 plots received only T. evanescens.

Materials used:

1-Bioinsecticide: Dipel 2x 6.4%Bacillus thuringiensis subsp.kurstaki strain applied at the recommended rate (200 g. /feddan)

2- T. evanescens was mass-reared at Rice Research Center (RRTC) laboratory (Kafr El-Sheisk Governorate) on eggs of grain moth, Sitotrogacerealella using the procedures described by Abbas (1998).

3-Release of T. evanescens:Release of T. evanescenstook place, on August, 30^th and September, 9^th in 2018 and on September, 2^nd and 10^th 2019.   Two different developmental stages of the parasitoid (larvae and old pupae in A.Kuehniella eggs) were mixed and released. Each plot (130 m²) received two releases at a rate of one card (850 eggs)/ release, indicating a rate of approximately 55,000 wasps /feddan. Each card was hanging to plant.  To avoid the spoil of the Parasitized eggs by insect predators, the edge of carton was fixed in a way, which helps escaping of the emerging parasitoids but prevent entrance of predators.

1-To estimate the percentages of parasitism:  Egg-masses of O. nubilalis were collected weekly from samples of 10 maize plants chosen randomly from the four treatments during the ovipositional activity period. Eggs of each mass were counted and placed in a 2× 10 cm. glass tube tightly closed on the top by muslin wrapped cotton plug and examined daily. Eggs that showed evidence of O. nubilalis larvae were categorized unparasitized while those   exhibiting the characteristic blackening caused by parasitism were considered parasitized.

2- In both of the two season’s studies, the population density of O. nubilalis larvae in different treatment started after one week of release parasitoids. Weekly random collection   of 15   maize plants   from each treatment were externally examined   and the   immature larvae were counted. In addition, each stalk was split and the number of O. nubilalis larvae was recorded.

3- At harvest, the rate of infestation in ears was estimated in40  random collection samples representing each treatment. Ears were categorized as infested by the presence of larvae or damage caused by larvae. 

RESULT AND DISCUSSION

Prediction of the oviposition time:

Weekly examined of maize plants started after 35 days from sowining. Egg mass counts gradually increased reaching the peak on September 5^th 1998 and September 10^th 1999.

  As a result, two releases of the parasitoid were carried out at a rate of 33000 parasitoids per feddan as old pupae and larvae at 7 days interval (August 28^th and September, 9^th in 2018 and on September, 17^th in 2019). One application of B. thuringiensis was also made in the same date of the first release in each year.

Percentages of parasitism in O. nubilalis eggs in different treatments 

  The release of parasitoids dramatically affected the fate of O. nubilaliseggs in different plots (TrichogrammaandTrichogramma + Dipel) in 2018 and 2019 (Tables 1 & 2). In release plots, there was an increase in the parasitized eggs and a decrease in the egg hatching, due to increasing the natural role of the parasitoid. The percentages of parasitism were 72.87 and 70.69 % in plots received TrichogrammaandTrichogramma + Dipel compared to 35.12and 37.76 % for control and Dipel treatments, respectively in 2018 season.

Similar results were obtained during 2019; the percentages of parasitism were 75.12 % in the Trichogrammarelease plots and 73.76 % in Trichogramma +Dipel, compared to 33.69 % and 39.17 %, in the control and Dipel treatments, respectively. It is assumed that high temperature increased the impact and activity of these parasitoids   in   the two years of study (means of temperature and R.H. were 30.3 ^°C and 55 % in 2018 and 32.2 ^°C and 60 % R.H. in 2019).

Rate of damage caused by O. nubilalis

      Population density of O. nubilalislarvae

  Larvae of O. nubilaliswere counted weekly in 15 maize plants chosen randomly from each treatment. Data obtained and presented in Table (3) clearly indicated that   maize plants of control plots received the highest mean number of O. nubilalislarvae (106 and 117.7 larvae per 15 plants in 2018 and 2019 Nili plantation, respectively). On the other hand, the lowest mean numbers of larvae (30 and 39.8 larvae) was observed within the combined treatment of B. thuringiensisand Trichogramma. . The mean number of larvae in the plots, which received the parasitoids only, were 36.4 larvae in 2018 and 41 larvae in 2019. The corresponding figures in case of the treatment by B. thuringiensiswere 73.2 and 77.4 larvae / 15 plants in the two years, respectively.

According to (L.S.D.) values of the two years, the tested treatments could be arranged according to efficacy in descending order as; Trichogrammawith B. thuringiensis, Trichogramma; B. thuringiensis and control. Such data indicated significant differences between the control and the other three treatments. Insignificant differences were detected between the two treatments that received parasitoid releases (Trichogrammaonly and Trichogramma+ B. thuringiensis). Data indicated that the sole treatment by B. thuringiensisproved to be insufficient to prevent the larval attack.

Table (1): Percentages of parasitism of O. nubilalis eggs in Trichogramma evanescens release and non-release sites during 2018 season.

Table (2): Percentages of parasitism of O. nubilalis eggs in Trichogramma evanescens release and non-release sitesduring 2019 season.

Table (3):  Ostrinianubilalis larvae / 15 maize plants from different treatments in 2018 and 2019 Nili maize plantation.